1. Field of the Invention
This invention relates to a coupling unit for use between two shafts. It relates particularly to a coupling unit for transferring torque between two shafts which may be aligned at varying angles with each other and at the same time may be loaded with strong axial pressures. The invention relates particularly to means for driving so-called screw pumps for which a coupling unit is desirable which is capable of transferring torque between shafts which vary in their alignment with each other.
2. Description of the Prior Art
A screw pump consists of a rotatable screw, a rotor, which usually is made of a metallic meterial and which is arranged within a cylinder with a screw shaped inner surface made of resilient material, called the stator.
Due to the construction of a screw pump the rotor, when rotating, makes an oscillating movement, which means that the rotor shaft and the drive shaft during rotation will form an angle with each other, which angle changes continuously.
When working, relatively strong axial forces also occur between the rotor and the stationary part which forces must be carried by the coupling between the rotor and the driving shaft.
In screw pumps having relatively small dimensions it is possible to transfer the turning torque by help of a rigid shaft, a so-called torsion bar. The torque and bending forces in such a pump are so limited, that a solid bar of this type may be acceptable.
In bigger screw pumps, however, other power transfer devices are needed. In such cases it is known to use universal joints of different sorts, Oldham Joints, Crass-slide Joints and others. Common to all these types of couplings is the fact that they can transmit relatively large forces. The disadvantages include the facts that they are relatively complicated, require a lot of space, and are expensive to manufacture. Even their durability in many cases is too poor to provide an acceptable dependability, especially when they are subjected to strong axial forces.